Objective: Intensified management of gestational diabetes mellitus can normalize birth weight. However, it is still unknown whether intrauterine exposure to maternal diabetes is a risk factor for changing hormone levels involved in the development of insulin resistance in these infants. We compared insulin and leptin levels in appropriate for gestational age (AGA) infants of diabetic and non diabetic mothers. Methods: We performed a cross-sectional study in the department of Neonatology of the Hospital of Gynecology-Pediatrics, in Leon, Mexico. We evaluated 182 full term AGA newborns (86 infants of diabetic and 96 of non-diabetic mothers). A venous blood sample was taken from cord blood immediately after the separation of the placenta and glucose, insulin and leptin levels were measured. In all diabetic mothers HbA1c was also evaluated immediately post-partum. Findings: Leptin, insulin and insulin resistance index were significantly higher in infants of diabetic mothers. Leptin levels were positive correlated with insulin, parents‘ body mass index and age in the entire group. In infants of diabetic mothers only insulin levels showed a significantly correlation, whereas in those of non-diabetic mothers only mothers‘ age was significantly correlated with leptin levels. Conclusion: AGA infants of diabetic mothers showed higher leptin, insulin levels and insulin resistance index than those of non-diabetic mothers.